Analog Multiplierless LMS Adaptive FIR Filter Structures

Two adaptive FIR filter configurations are proposed for implementing the LMS algorithm with no along delay elements or multipliers. The first uses a linear feedback shift register (LFSR) to generate pseudorandom binary sequences for applications where white noise has been traditionally used. The binary signals are delayed by a shift register and multiplied by on/off switching so that the resulting structure is free of analog delay lines and multipliers. For applications where inputs are colored, the second configuration uses a Σ-Δ modulator as front-end for converting the adaptive filter's input into a binary sequence. Such a filter tends to adapt itself into a low-pass characteristic to remove the high frequency noise due to the modulator.